The impact of endolymphatic hydrops on wideband acoustic immittance and otoacoustic emissions in guinea pigs

Background

Inner ear disorders, such as EH, commonly lead to hearing loss and vestibular dysfunction. EH is particularly prevalent in various inner ear diseases, including Meniere's disease. We aimed to evaluate the effects of EH on WAI and OAEs.

Objective

This study explores the potential of wideband acoustic immittance (WAI) and otoacoustic emissions (OAEs) for the early detection of changes in acoustic transmission associated with vasopressin-induced endolymphatic hydrops (EH) in a guinea pig model.

Methods

We induced EH in guinea pigs via daily intraperitoneal injections of arginine vasopressin over 14 consecutive days. Auditory function was assessed using Auditory Brainstem Responses (ABR), while changes in sound energy transmission were measured using WAI and Distortion Products Otoacoustic Emissions (DPOAE).

Results

Increased ABR thresholds in EH models were statistically significant (p < 0.05). After 14 days of EH induction, absorbance at 1 kHz significantly increased, whereas it significantly decreased at 4 kHz and 6 kHz (p < 0.05). DPOAE measures, both magnitude and phase, showed no significant changes (p > 0.05).

Conclusion

WAI demonstrates greater sensitivity than DPOAE in the early detection of acoustic transmission alterations in EH models, suggesting its utility as a diagnostic tool in early-stage inner ear disorders.

Audiologic Profiles of Children With Otitis Media With Effusion

OBJECTIVES

To describe the impact of effusion volume, viscosity, and purulence on the audiologic profiles of children with otitis media with effusion.

DESIGN

Fifty-one ears from children between the ages of 8 months and 11 years who had a diagnosis of otitis media with effusion and were scheduled for tympanostomy tube placement were recruited from medical clinics. The control group consisted of 17 ears from children between the ages of 10 months and 11 years without a recent history of otitis media and were recruited from a database of research volunteers. Participants received a comprehensive audiologic testing battery consisting of tympanometry, otoacoustic emissions, behavioral audiometric thresholds, and auditory brainstem response testing. For children with otitis media, this testing battery occurred 1 to 2 days before surgery. Middle ear effusions were characterized and collected on the day of surgery during tympanostomy tube placement from ears with otitis media with effusion. The comprehensive audiologic testing battery was completed postoperatively as well for most participants.

RESULTS

Effusion volume, categorized in each ear as clear, partial, or full, effected the audiologic results. Ears with full effusions had moderate hearing losses, few to no measurable otoacoustic emissions, and delayed Wave V latencies. Ears with partial effusions and clear ears both had slight to mild hearing losses and normal Wave V latencies, though ears with partial effusions had fewer measurable otoacoustic emissions than clear ears. Normal-hearing control ears with no recent history of otitis media with effusion demonstrated normal audiometric thresholds, present otoacoustic emissions, and normal Wave V latencies. Repeat postoperative testing demonstrated improvements in audiologic testing results for all of the otitis media with effusion volume groups, with no significant differences remaining between the three otitis media with effusion groups. However, significant differences between otitis media with effusion ears and normal-hearing control ears persisted postoperatively, with otitis media with effusion ears demonstrating significantly poorer audiometric thresholds and reduced otoacoustic emissions as compared to normal control ears. The effect of effusion viscosity and purulence could not be systematically evaluated because minimal variability in effusion viscosity and purulence was observed in our sample, with nearly all effusions being mucoid and nonpurulent.

CONCLUSIONS

Effusion volume observed at the time of tympanostomy tube surgery was found to play a significant role in outcomes and responses on a range of audiologic tests that compose the standard clinical pediatric audiologic assessment battery. Full middle ear effusions were associated with a moderate hearing loss, and few to no measurable otoacoustic emissions were detected. Ears with a recent diagnosis of otitis media with effusion but clear at the time of tympanostomy tube placement had less hearing loss and a greater number of present otoacoustic emissions than ears with full or partial effusions but were still found to have poorer hearing sensitivity than the healthy control ears. Differences between ears with otitis media with effusion and healthy control ears persisted on postoperative assessments of otoacoustic emissions and audiometric thresholds, though there were no remaining effects of the presurgical effusion volume group.

High-frequency otoacoustic emissions in universal newborn hearing screening

OBJECTIVE

Distortion-product otoacoustic emissions (DPOAEs) are currently used in many newborn hearing screening programs as the initial hearing test, typically testing frequencies between 1 and 4 or 6 kHz, but they have been associated with high false-positive rates. The objective was to investigate the possible benefit of high-frequency DPOAEs for reducing false-positive rates.

METHODS

255 healthy newborns (138 males and 117 females) undergoing conventional hearing screening based on DPOAE and automated auditory brainstem response (AABR) testing were recruited. High-frequency DPOAE amplitudes, noise floors and signal-to-noise ratios (SNRs) were measured for f2 frequencies up to 12 kHz.

RESULTS

Of the 255 newborns who participated in this study, 23 (9%) failed the conventional DPOAE test but passed the AABR test, and 8 (3%) failed both tests. For an SNR threshold of 6 dB, high-frequency DPOAE tests at f2 = 4, 6, 8 and 10 kHz resulted in a reduction in the false-positive rate from 9% to 0.4%, or to zero if only three of the four frequencies were required to exceed the threshold. SNRs were lower in newborns with birth weights greater than 4000 g; lower at 2 kHz in newborns with a gestational age of 41 weeks; slightly higher in vaginally-delivered newborns; and higher at 2 kHz with increasing age in the group that failed the conventional DPOAE test but passed AABR.

CONCLUSION

High-frequency DPOAEs resulted in a reduction in the DPOAE failure rate and the false-positive rate. These findings may be helpful in universal newborn hearing screening programs.

Factors affecting sound energy absorbance in acute otitis media model of chinchilla

Acute otitis media (AOM) is a rapid-onset infection of the middle ear which results in middle ear pressure (MEP), middle ear effusion (MEE), and structural changes in middle ear tissues. Previous studies from our laboratory have identified that MEP, MEE, and middle ear structural changes are three factors affecting tympanic membrane (TM) mobility and hearing levels (Guan et al., 2014, 2013). Sound energy reflectance or absorbance (EA) is a diagnostic tool increasingly used in clinical settings for the identification of middle ear diseases. However, it is unclear whether EA can differentiate these three factors in an AOM ear. Here we report wideband EA measurements in the AOM model of chinchilla at three experimental stages: unopened, pressure released, and effusion removed. These correspond to the combined and individual effects of the three factors on sound energy transmission. AOM was produced by transbullar injection of Haemophilus influenzae in two treatment groups: 4 days (4D) and 8 days (8D) post inoculation. These time points represent the relatively early and later phase of AOM. In each group of chinchillas, EA at 250-8000 Hz was measured using a wideband tympanometer at three experimental stages. Results show that the effects of MEP, MEE, and tissue structural changes over the frequency range varied with the disease time course. MEP was the primary contributor to reduction of EA in 4D AOM ears and had a smaller effect in 8D ears. MEE reduced the EA at 6-8 kHz in 4D ears and 2-8 kHz in 8D ears and was responsible for the EA peak in both 4D and 8D ears. The residual EA loss due to structural changes was observed over the frequency range in 8D ears and only at high frequencies in 4D ears. The EA measurements were also compared with the published TM mobility loss in chinchilla AOM ears.